import {count, add} from './calculator.js'

console.log(count); // 0 (对calculator.js中count值的映射)

add(2, 3)

console.log(count); // 1 (实际反映calculator.js中count值的变化)

count += 1; // 不可更改, 会报出SyntaxError: "count" is read-only

